Rising energy costs and more stringent legislation governing the permissible fuel consumption or permissible noxious emissions of motor vehicles containing internal combustion engines necessitate measures to, on the one hand, reduce the fuel consumption of internal combustion engines and, on the other, insure that the noxious emissions produced by the motor vehicle assume low values. It has in this regard become known how to operate internal combustion engines, in particular gasoline-operated engines, in certain phases of their operation by means of an auto-igniting combustion method that is also referred to as Homogeneous Charge Compression Ignition (HCCI), Compressed Auto Ignition (CAI), or Chamber Ignition (CI). With said auto-igniting combustion method, auto-igniting, and hence the course of combustion, is controlled via the reactive amount of energy in the cylinder of the internal combustion engine. Said amount of energy can be provided by, inter alia, what is in comparison with the conventionally operated spark ignition engine a very high proportion of residual gas. It is known also in the case of conventionally operated spark ignition engines how to operate the internal combustion engine in the lower and mid underload range at a high exhaust gas recirculation rate in order to optimize combustion in terms of the quality criteria “consumption” and “emissions”.
A method for determining the curve of a combustion chamber pressure in an internal combustion engine is known from DE 199 007 38 C1. Said method entails obtaining an estimated value of a cylinder pressure as a function of a previously obtained measured value of the cylinder pressure, of a volume, assigned thereto, of the cylinder, and of a volume, assigned to the estimated value of the cylinder pressure, of the cylinder, and of a polytropic exponent by means of the polytropic equation. The polytropic exponent is predefined as a function of a coolant temperature.
A further method for determining the combustion chamber pressure in a cylinder of an internal combustion engine is known from EP 0 399 069 A1. A sensitivity of the cylinder pressure sensor assigned to said internal combustion engine is determined for this purpose in each operating cycle of the cylinder, specifically as a function of three voltage measurement signals and a predefined polytropic exponent.